In a typical cellular network, User Equipments (UEs), communicate via a Radio Access Network (RAN) connected to one or more Core Networks (CNs).
A user equipment is a mobile terminal by which a subscriber can access services offered by an operator's network. The user equipments may be for example communication devices such as mobile telephones, cellular telephones, laptops or tablet computers, sometimes referred to as surf plates, with wireless capability. The user equipments may be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station or a server such as a content providing server. User equipments are enabled to communicate wirelessly in the cellular network.
The cellular network covers a geographical area which is divided into cell areas. Each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. Multimedia Broadcast Multicast Service (MBMS), an example of a broadcast service, is a point-to-multipoint interface specification for existing and upcoming 3GPP cellular networks. MBMS is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network. For broadcast transmission across multiple cells, it defines transmission via single-frequency network configurations.
Target applications comprise mobile TV and radio broadcasting, as well as file delivery and emergency alerts.
Multimedia Broadcast Multicast Service (MBMS) was introduced in 2005 for different types of Radio Access Networks (RAN), i.e. for Global System for Mobile Communications (GSM), for Enhanced Data Rates for GSM Evolution (EDGE) RAN (GERAN), and for Universal Terrestrial RAN (UTRAN) Rel-6 and in 2010 for Evolved UTRAN (E-UTRAN) Rel-9 for more efficient distribution of identical services, i.e. services that are identical for several users.
For MBMS, two new logical channels were introduced: First, the Multicast Control Channel (MCCH), which carries information about MBMS specific transport channel configurations, in E-UTRAN (also referred to as Long Term Evolution of UMTS or in short, LTE) the Multicast Channel (MCH), and the corresponding MBMS services. Second, the Multicast Traffic Channel (MTCH), which carries the MBMS data of a service. The MCCH contains information for the User Equipment (UE) to be able to read a specific MBMS service. Both MCCH and MTCH are mapped to one or more MCHs. In E-UTRAN, SystemInformationBlockType13, in short SIB13, which is cell specific, contains information about MCCH configuration and scheduling, such that the UE can find and read the MCCH.
For MBMS, broadcast services are generally offered within a large geographic area, consisting of one or more cells. In order to exploit this, these cells apply MBMS single frequency network (MBSFN) operation, which means that identical signals are transmitted on the same time-frequency radio resources from each cell, such that the received signal power in the terminal is increased. The cells that offer the same set of MBMS services and the same scheduling of MBMS service sessions belong to one MBSFN area. The cells within the same MBSFN area transmit all MCHs within this MBSFN area in MBSFN mode, i.e. the corresponding MCCH and all MTCHs.
In order to achieve MBSFN operation, one essential requirement is that the cells which belong to the same MBSFN area are tightly synchronized (e.g. in the order of micro-seconds). From a terminal perspective all signals transmitted from the cells within the MBSFN area combine over the radio resulting in an improved signal to interference and noise ratio (SINR). If the cells within an MBSFN area are very close to each other, the aggregated SINR will be unnecessarily high. Therefore, 3GPP introduced MBSFN area reserved cells, which do not contribute to the MBSFN transmission and therefore do not advertise its availability. Furthermore, MBSFN area reserved cells are allowed to transmit other services on the resources allocated for the MBSFN transmission, but only with restricted power to avoid an inacceptable SINR of the MBSFN signal.
As the reserved cells do not transmit the broadcast service, the base station controlling the reserved cell requires less transmit power, which supports the idea of power efficient radio networks. Still there is a wish that a UE that is served by a reserved cell is provided with the broadcast service in a robust and efficient way. So, it is an object to provide improved methods and base stations for supporting a broadcast service within a cell of a base station that is not transmitting the broadcast service. It is an object to improve the quality of the broadcast service, to lower interference in cellular systems and to increase efficiency in using the radio resource. It is an object to help saving transmit power in a radio network.